Artists Who Are Not In The Rock Hall

But Should Be

Grand Funk Railroad

Jethro Tull

Devo  

Blue Oyster Cult

King Crimson

Smashing Pumpkins

Warren Zevon

Emerson, Lake and Palmer (these guys sold out stadiums!)

Supertramp

Bachman Turner Overdrive

The B-52s

Kansas

Styx

War

The Smiths

Boston (or at least Tom Scholz)

Joe Cocker

Canned Heat (like Paul Butterfield, they spearheaded a blues revival)

The Guess Who

Iron Maiden

Steppenwolf

Peter Frampton (best selling live album of all time!)

Steve Winwood

Joe Walsh

There are lots of newer bands as well, but these are the biggest oversights in my opinion.